If Microbes Are Not Capable of Growth as Pure Isolated

If microbes are not capable of growth as pure isolated cultures,which factor do you consider the most likely to contribute to the growth challenge?

A) Unculturable microbes may receive essential nutrients as a result of the metabolic activity of another member of a mixed microbial community
B) Nutrients not yet identified by bioscientists may be lacking from a defined growth medium
C) Gene transfer from other microbes may be required for active growth
D) RNA transfer from other microbes may be required for active growth
E) Protein transfer from other microbes may be required for active growth